1. Field of the Invention
The present invention relates to a coating treatment method for a substrate, such as a semiconductor wafer and the like.
2. Description of the Related Art
In the photolithography process in manufacture of a semiconductor device, a resist coating treatment of applying a resist solution, for example, onto a semiconductor wafer (hereinafter, referred to as a “wafer”) to form a resist film is performed. As the coating treatment method, the spin coating method is generally employed. The spin coating method is a method of supplying a resist solution R from a nozzle 11 to the central portion of the front surface of the wafer W with the wafer W sucked to a spin chuck 10 as shown in FIG. 12, and rotating the spin chuck 10 at a high speed so as to spread the resist solution R outward in the radial direction of the wafer W by the centrifugal force.
To perform such a resist coating, it is necessary to apply the resist solution onto the wafer with high in-plane uniformity.
Incidentally, since miniaturization of the pattern of the semiconductor device and reduction in film thickness are required, various resist solutions adaptable to such photolithography are developed. However, the cost of the resist solutions is rising more than before because the resist solutions are required to have precise physical properties, so that the resist solutions are very expensive in the present circumstances. Therefore, the consumption of the resist solution needs to be further reduced, and accordingly a coating method is desired which can save the resist more than before and ensure a high in-plane uniformity for the film thickness.
Hence, according to a conventionally proposed resist coating method, the solvent for the resist solution is used to pre-wet the top of the wafer, and the resist solution is supplied to the wafer while the wafer is rotated at a first number of rotations, so that the resist solution is applied spreading outward in a direction of the radial of the wafer. Immediately after stop of the supply of the resist solution, the wafer is decelerated to a second number of rotations to adjust the film thickness, and then accelerate to a third number of rotations to shake off the remaining solution (Japanese Patent Application Laid-open No. H11-260717). In this case, specifically, the first number of rotations is 4500 rpm, the second number of rotations is 500 rpm, and the third number of rotations is 3000 rpm.
However, when the supply amount of the resist solution is small, the resist solution has sometimes not fully spread to the edge of the wafer while the wafer is rotated at the first number of rotations because of a weak centrifugal force exerted on the resist solution. In this case, the resist solution has been further spread while the wafer is rotated at the third number of rotations so that the resist solution is applied over the entire wafer. In the case where the resist solution is spread separately at two stages as described above, the resist solution dries to decrease in flowability during the rotation of the wafer at the second number of rotations and therefore is different in speed of spreading on the wafer between the case when the wafer is rotated at the first number of rotations and the case when the wafer is rotated at the third number of rotations. More specifically, in the case of the wafer with a diameter of 300 mm, the film thickness of the resist film may be different between the outside and the inside with a circle with a radius of 120 mm as a boundary (occurrence of a so-called polarization of the film thickness), resulting in reduced in-plane uniformity of the film thickness.